Radio control system



Dec. 29, v1942.

E. B. BERGLUND RADIO CONTROL SYSTEM 2 Sheets-Sheet 1 Filed Aug. 50, 1941www E. B. BERGLUND 2,306,858

RADIO CONTROL SYSTEM Filed Aug. 50,-l94l 2 Sheets-Sheet 2 Dec. 29,"1942.

INVENToR l mfc/(. amsn/No BY )KZ ATroRNEY Patented Dec. 29, 1942 unirse:sTATEs garant ori-'lcs RADIO'N SYSTEM Erick B; Bergl'und', Garden City,N. Y., assigner to Radio Corporation of America, a corporatlon ofDelaware Application August'30, 1941, Serial No. 409,005

5 Claims.

The present invention relatestdthecontrol of'.. and mixing of, a.plurality of. diierent. audio frequency currents and, more particularly;toradio broadcasting wherein a. radio wave is modulated in accordance:with the currents from a plurality of separate microphone circuits.

In broadcastingcertain types oi programs such. as, for example..speeches in a foreign language sports events, etc., it is sometimes.desirablev for an` interpreter or a commentator tov inter.-y polate aninterpretation orv comment the main program during the time when it isbeing; presented. In accordance with the present invention theinterpreter, or commentator, operates akey switchv fading the-mainprogram to` an-un- Ji" obtrusive level and simultaneously cutting in hisown microphone. During the time the interpola.- v

tions are hea-rd the main program may be heard in: the background. Afterthe comments are ccmpletedfrelease-of the key switch restoresf-the mainprogram to-fullvolume level at a predeter` mined rate. The fadingy rateof the-mains-pro gram and its recovery time is controllable so` that.the. switching isnot disagreeablynoticed:byv l the listening audience.

An object ofthe present inventioniisftheproevision of afcircuitarrangement for readily; pere forming theabove lmentionedoperations..

Another objectV of the present' invention: is the provision of anarrangement, as aforesaid..

vention, and Figure 2 isaa curve illustratingfth'e variations.r4 in thedifferent sig-naly levels in" the output ci.- the'dev-iceY ofk Figurel'.

ltceferring,v now, toFigure 1, there is shownat ifi4 an inputtransformer or coupling-1 meansy for coupling aV program circuit-to asrst: amplifier. tubeal Theprogramcircuit which-may be eX- tended'from aVpointzremote from :the'usual':broadL cast studios-is, under suchcircumstances,. corn-- menly known as avnemo, circuit andthefinfputis,.,therefore,labellednemoinputf Tube I Ii,.

through output transformer I8.

which is shown as a triode connected pentode tube, may be a triode or itmay be operated asa pentode amplifier as, circumstances require. Avolume control I2' in the grid circuit of tube `II is provided tocompensate for variations in level of the input signal. Tube I I isshown as having its grid biased by means of a cathode resistor I3 and aby-passV condenser I4 though, of course, a grid bias battery may be usedinstead, if desired. Between the anode of tube II and the positive anodesupply source B+, is connected a plate load resistor I5. Coupled to theanode end of resistor lE-b-y means of condenser I6 isV the control gridcircuit of a super control pentode amplier tube Il. This tube is usedbecause of the fact that control: grid bias variation is capable ofvarying the amplication thereof over a wide range. The anode of tube Ilis connected to the positive anode supply source B+,

Output transformer I8 is coupled through fader 3l to the input ofampliiier Sli. The output of amplier 34 is coupled by conventionalcircuit means to the desired modulating equipment for modulating thebroadcast radio wave.

The screen potential for tube I'I is supplied by a voltage dividercomposed of resistors I9 and 20connected across the anode supply source.A standing bias is applied to tube Il by means of cathode resistor 2i.In the grid circuitV of tube Il are serially connected resistor 22 andcondenser 23. To the junction between resistor 22 and condenser 23 isconnected a resistor 24, the other end of which is connected to contacts25` of relay'Z. Contacts 25are arranged to selectively connect resistor24 to B- or ground through variable' resistor 2l or through aselooted-portion of battery 2t. The positive pole of battery 28 isgrounded and by means of selector switch 21S-different values ofnegative potential may be connected to relay contacts 25.

Relay 2,6. in addition to operating contacts 25, operatescontacts 35which are connected in a channel 301to complete the channel circuit whenrelay 25 is operated. Channel 30 at'its input is coupledlto. amicrophone circuit for the use of the interpreter orcommentator and atits output end is coupled through fader 33 to amplifier 34. The windingof relay 26 is energized from battery 35 whenever key 3l is operated. Acable is indicated in the circuit between key 3l and the remainder ofthe energizing circuit for relay 26 inorder to indicate that the key 3lmay be placed' at any requireddistance from the remainder ofYthevcircuit.l Usually, ke;7 3l will` be'y located on the desk of thecommentator or interpreter whose comments are to be interpolated intothe program carried by the nemo channel. Resistors 4l and 42 areconnected across the contacts 35 in order to prevent disturbing clickswhen the contacts are opened or closed. In the operation of the circuitas described, when the key switch 31 is in the open or foreign position,relay 26 disconnects the interpolator channel 3B through the opening ofcontacts 35 and connects the junction between resistor 22 and condenser23 to ground through resistors 24 and 21. The amplifier tube i1 thusoper-ates at its standing bias Value determined by resistor 2| and thenemo program is fed through amplifler tube H, tube I1 throughtransformer I8, fader 3! into the input of amplifier 34 and thence outto its ultimate destination. Tube i1, as mentioned, operates as a normalamplier with normal bias on its grid. When the key switch 31 is closedto its interpolation position, relay 26 is energized thus closingcontacts 35 completing the interpolator channel 3Q and applying a largenegative bias from battery 28 to the junction between resistor 22 andcondenser 23 and therefore to the control grid of tube l1. This fadesthe level of the nemo program a definite lower value depending upon theamount of bias applied to the grid of tube I1 by means of selectorswitch 29. The time required for the fade to become completely eifectivedepends upon the time constant of resistor 2li and condenser 23.Ordinarily, this is adjusted to be of the order of a half second. Theinterpolator channel 30 being completed, the voice of the interpreter isapplied at a full level determined by fader 33 to amplifier 34 and theforeign program is transmitted at a reduced level through fader 3l toamplifier 344. After the interpreter, or commentator, has finished hiscomments, key switch 31 is released and the interpolator channel 30 isimmediately disconnected. The de-energization of relay 2S operatescontacts 25 to a series circuit comprising resistors 24 and 21 acrosscondenser 23. The time constant of the circuit including resistors 24and 21 across condenser 23 determines the time of recovery of theamplifier tube l1 to its normal gain value. The time delay is variablebetween one-half and two seconds by varying the value of variableresistor 21.

Figure 2 illustrates in curve form the relationship between the volumelevels of the nemo program and the interpolator program at the inputs offaders 3l and 33 before, during and after actuation of key switch 31. Inpart l, when the key switch is open, it will be noted that the nemooutput indicated by solid line 45 is adjusted to a level of -16 VU byfader 3l. The output of the interpolator channel is absent since itscircuit is open. At the end of part 1 the key switch 31' is operated andthe interpolator output, as indicated by dotted line 46, instantaneouslyrises to the same level as that of the nemo output, that is, 16 VU. Inthe first one-half second following the operation of key switch 31 thenemo outputI level drops to a predetermined value which may be either13, 18 or 23 db. below the normal level, depending upon the position ofswitch 29. This relationship is maintained during the entire periodduring which key 31 is closed. At the end of part 2, the key switch 31is opened and the output of the interpolator channel 3i) immediatelydrops to zero. Due to the time constant of the combination of resistors24 and 21 and condenser 23, the gain of amplifier l1 is graduallyrestored so that the nemo .output again attains its normal value of 16VU. In Figure 2 this time period is labeled part 3 and, as indicated,may be adjusted to any value between one-half second and two seconds.

With the nemo amplier output and the interpolator output directly underthe control of the commentator or interpreter by means of key switch 31the interpolation of comments and the fading of the nemo program can beperfectly synchronized without the difficulties encountered Where thechannel switching and fading is under the control of an engineeroperating in response to eues or signals from the commentator. This isespecially true in the case of unrehearsed foreign programs.

While I have particularly shown and described several embodiments of myinvention, it is to be clearly understood that my invention is notlimited thereto but that modifications may be made within the scopeofthe invention.

I claim:

1. In combination, a pair of channels for audio frequency currents,means for combining said channels into a single output circuit, anamplier in one of said channels, the other of said channels beingadapted to be connected to a microphone and having a normally openswitch therein, and means at the location of said microphone and subjectto manual control by a speaker for simultaneously operating said switchto complete said other channel and for gradually decreasing the gain ofsaid amplifier to a predetermined level, said means, upon release,opening said switch and gradually restoring the gain of said amplifier,the rate of said restoration being substantially less than the rate ofsaid decrease.

2. In combination, a pair of channels for audio frequency currents,means for combining said channels into a single output circuit,transducer means in one of said channels, the other of said channelsbeing adapted to be connected to a microphone and being normallydiscontinuous, means at the location of said microphone and subject tomanual control by a speaker for simultaneously establishing continuityin said other channel and for gradually decreasing the effectiveness ofsaid transducer means to a predetermined level, said means being furtheroperative to restore discontinuity to said other channel and togradually restore the eifectiveness of said transducer means and furthermeans for controlling the rate of said restoration.

3. In combination, a pair of channels for audio frequency currents,means for combining said channels into a single output circuit, anamplifier tube in one of said channels, said amplifier tube having astanding bias on a control electrode thereof, the other of said channelsbeing adapted to be connected to a microphone and having a normally openswitch therein, and means at the location of said microphone and subjectto manual control by a speaker for simultaneously operating said switchto complete said other channel and for gradually increasing said bias onsaid tube to reduce the gain thereof to a predetermined level, saidmeans, upon release, opening said switch and gradually decreasing thebias on said tube to its standing value.

4. In combination, a pair of channels for audio frequency currents,means for combining said channels into a single output circuit, anamplifier in one of said channels, the other of said channels beingadapted to be connected to a microphone and having a normally openswitch therein, means at the location of said microphone and subject tomanual control by a speaker for simultaneously operating said switch tocomplete said other channel and gradually decreasing the gain of saidamplifier to a predetermined level, said means, upon release, openingsaid switch and gradually restoring the gain of said amplifier andfurther means for controlling the rate of said restoration.

5. In combination, a pair of channels for audio frequency currents,means for combining said channels into a single output circuit, means insaid channels for controlling the transmission

